Hitherto, organic acids or its salts and glycol series pastes have been principally used as an electrolyte for electrolytic capacitor in the general purposes. The latest expansion of utilization for the electronic instruments requires more improvement and advancement in the reliability and performance of the capacitor entailing undesired problem of the presence of water in the paste and as a result an electrolyte using an aprotic solvent in place of organic acid and its salt and glycol paste has become to receive an attraction.
The greatest subject of employment of the aprotic solvent system electrolyte is how to obtain an electrolyte of high conductivity and to achieve this an organic carboxylic acid or its salt which is well soluble in the aprotic solvent and has a high degree of dissociation has been researched as a main work but not yet succeeded. To solve the matter and obtain a high conductivity a solvent which produces water resulted by the reaction between acids and alcohols or glycols and even water is incorporated into the aprotic solvent with still insufficient conductivity, increments of water and solute contents with poor reliability at the elevated temperature as disclosed in the Japanese patent publications Nos. 55-3989, 57-56763, 58-32769 and the U.S. Pat. No. 4,117,531.
After extensive researches and studies to obtain an electrolyte which is substantially nonaqueous system electrolyte and has a high conductivity with use of an aprotic solvent but without using any solvent which forms water in reaction between acids and alcohols with glycols, it has been discovered that a tetrafluoroboric acid salt of a pyrylium or thiopyrylium compound has a high solubility in the aprotic solvent with an enhanced releasability and provide a high conductivity.